Typical radio paging systems provide simple unidirectional transmission from a fixed location to a specifically addressed portable pager, such that when the transmission is received, the pager device provides an alerting tone, a simple text message, or both. Paging systems provide optimized one-way communication over a large region through a high power transmitter, typically a few kilowatts, that uses high antennas at multiple sites to provide reliable coverage throughout the region. Satellite-based paging systems are also in operation to provide extended service regions. The power requirements of a pager are typically very low because the pager is often simply a receiver with a small annunciator. A pager is, therefore, a small, light weight and relatively low cost device, which can operate for long intervals before its batteries need to be recharged or replaced.
Due to the advantage in size, cost and operating duration offered by pocket-size pagers, attempts have been made to impart limited two-way communication into paging systems, which are optimized for one-way traffic. One known attempt includes the incorporation of an acknowledgement message through reverse transmission links between the individual pagers and the fixed sites. Another known reverse-paging approach includes the use of codes corresponding to a series of messages, which may be tailored to a particular user. When the user wishes to send one of the messages, he activates his pager, types in the code corresponding to the predetermined message and a further code which indicates the destination of the message. A CPU associated with the fixed site receives the signals transmitted by the pager and determines the codes which have been transmitted. The CPU can then send the messages indicated by the codes to the desired destination.
When responding to a page or received message, however, it is often desirable to refer to the text of the original message or a portion thereof. Including the text of the original message in the response by the recipient of the page, however, would typically result in a lengthy reply, thus requiring additional bandwidth which may not be available for use in transmitting a response from the pager. Also, transmitting a lengthy reply typically requires more power than a shorter reply. Furthermore, known existing paging devices do not provide for predetermined codes which the recipient of the original page can use to refer to specified portions of the received message, because the text of the original message is not known by the recipient in advance.
It is, therefore, desirable to provide a two-way paging system that allows the recipient of a message on a paging device to respond by including references to the text of the original message without significantly increasing the bandwidth required to transmit the response.